The common causes of leg thinning after ankle fracture include muscle atrophy and nerve injury caused by long time inactivity. 1. Prolonged inactivity: after ankle fracture, due to long-term splint or plaster fixation, bed rest, reduced weight-bearing activities, the lower limb muscles can not be trained, resulting in atrophy of the calf muscles, so the leg appears thin. 2. Nerve injury: it may also be due to the combination of nerve injury after fracture, so that the muscles of the lower limb lack of innervation, resulting in muscle atrophy, leading to leg thinning. After the fracture of the ankle bone legs become thin, may also be caused by other reasons, it is recommended to go to the hospital in a timely manner, under the guidance of the doctor for standardized treatment.